Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
  • C01B33/021—Preparation
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
  • C01B33/021—Preparation
  • C01B33/027—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material
  • C01B33/035—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material by decomposition or reduction of gaseous or vaporised silicon compounds in the presence of heated filaments of silicon, carbon or a refractory metal, e.g. tantalum or tungsten, or in the presence of heated silicon rods on which the formed silicon is deposited, a silicon rod being obtained, e.g. Siemens process
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
  • C23C16/24—Deposition of silicon only
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
  • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
  • G01N21/64—Fluorescence; Phosphorescence
  • G01N21/6489—Photoluminescence of semiconductors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00

Definitions

• the invention relates to a method for determining a surface contamination of polycrystalline silicon.
• crude silicon is obtained by reducing silica with carbon in the arc furnace at temperatures of about 2000 ° C.
• the metallurgical silicon For applications in photovoltaics and in microelectronics, the metallurgical silicon must be cleaned. For this purpose, it is for example reacted with gaseous hydrogen chloride at 300-350 ° C in a fluidized bed reactor to a silicon-containing gas, such as trichlorosilane. This is followed by distillation steps to purify the silicon-containing gas.
• a silicon-containing gas such as trichlorosilane.
• This high-purity silicon-containing gas then serves as a starting material for the production of high-purity polycrystalline silicon.
• the polycrystalline silicon often called polysilicon for short, is usually produced by means of the Siemens process.
• a bell-shaped reactor (“Siemens reactor") thin filament rods of silicon are heated by direct current passage and a reaction gas containing a silicon-containing component and hydrogen is introduced.
• the filament rods are usually placed vertically in electrodes located at the bottom of the reactor, via which the connection to the power supply takes place.
• Two Filamanentstäbe are coupled via a horizontal bridge (also made of silicon) and form a carrier body for the silicon deposition.
• the bridging coupling produces the typical U-shape of the support bodies, which are also called thin rods.
• these polysilicon rods are usually further processed by mechanical processing into fragments of different size classes, optionally subjected to a wet-chemical cleaning and finally packaged.
• the polysilicon can also be further processed in the form of rods or rod pieces. This applies in particular to the use of polysilicon in FZ processes.
• Polycrystalline silicon serves as a starting material in the production of monocrystalline silicon by means of crucible pulling (Czochralski or CZ process) or by zone melting (floatzone or FZ process). This monocrystalline silicon is cut into slices (wafers) and after a variety of mechanical, chemical and chemo-mechanical processing in the semiconductor industry used to manufacture electronic components (chips).
• polycrystalline silicon is increasingly required for the production of monocrystalline or multicrystalline silicon by means of drawing or casting processes, this monocrystalline or multicrystalline silicon being used to produce solar cells for photovoltaics.
• the material is investigated, for example, for contamination with metals or dopants. A distinction is made between the contamination in the bulk and the contamination on the surface of the polysilicon fragments or bar pieces.
• Dopants (B, P, As, Al) are analyzed by photoluminescence according to SEMI MF 1398 on an FZ single crystal (SEMI MF 1723) produced from the polycrystalline material.
• FTIR Fast-Transform IR spectroscopy
• Bases of the FZ process are, for example, in DE-3007377 A described.
• a polycrystalline stock rod is gradually melted by means of a high-frequency coil and the molten material is converted into a monocrystal by seeding with a monocrystalline seed crystal and subsequent recrystallization.
• the diameter of the resulting single crystal is first conically enlarged (cone formation) until a desired final diameter is reached (rod formation).
• the single crystal is also mechanically supported to relieve the thin seed crystal.
• a disk (wafer) is cut off from the single-crystal rod produced from a polycrystalline silicon rod by means of FZ (SEMI MF 1723). From the pulled monocrystalline rod, a disk is cut out, etched with HF / HNO 3, rinsed with 18MOH of water and dried. The photoluminescence measurements are carried out on this disk.
• a slice is cut out of a polycrystalline rod.
• the slice is polished.
• the carbon content is determined by means of FTIR spectroscopy.
• Impurities on the surface can only be determined indirectly.
• DE 41 37 521 A1 describes a method for analyzing the concentration of impurities in silicon particles, characterized in that particulate silicon is placed in a silicon vessel, the particulate silicon and the silicon vessel work up to monocrystalline silicon in a suspension zone and the concentration Impurities that are present in the monocrystalline silicon can be determined.
• the concentrations of boron, phosphorus, aluminum and carbon in the silicon vessel used were determined and provide a reproducible background value.
• the values for boron, phosphorus and carbon determined by the FTIR using the floating zone method were corrected for the proportion that originated from the silicon vessel. In this application it is also shown that the fragmentation of a polycrystalline silicon rod leads to a contamination of the silicon.
• DE 43 30 598 A1 also discloses a method which makes it possible to deduce the contamination of silicon due to comminution processes.
• a block of silicon was broken into pieces.
• the silicon lump was then subjected to a zone melting process and converted into a single crystal.
• a wafer was sawn out and examined by photoluminescence for boron and phosphorus.
• photoluminescence for boron and phosphorus.
• concentration of boron and phosphorus which is also attributable, inter alia, to the comminution process.
• the described methods do not take into account that the environment in which not only the comminution process, but also other process steps such as storage, transport, cleaning, packaging take place, have an influence on the contamination of the silicon, in particular on its superficial contamination.
• two polycrystalline silicon rods are provided by depositing polycrystalline silicon in a Siemens reactor to form U-shaped polycrystalline silicon bodies each comprising two polycrystalline silicon rods.
• the reaction gas used in the deposition is typically a silicon-containing component, preferably trichlorosilane, and hydrogen.
• the deposition takes place in a small test reactor.
• a previously mentioned U-shaped body can be removed from the reactor after deposition, with the bridge and the respective bar ends subsequently being severed, so that two polycrystalline silicon rods are obtained in one and the same batch.
• the two polycrystalline silicon rods provided in step a) were preferably connected to one another during the deposition via a bridge (U-shape) (fret rods).
• the two polycrystalline silicon rods When using a small reactor, the two polycrystalline silicon rods typically have a length of about 20 cm and a diameter of about 1.6 cm.
• One of the two bars is preferably packed in a PE bag immediately after the separation and separation of bridge and bar end.
• both bars are each packed in a PE bag.
• This first rod is then examined for contamination.
• dopants and carbon are determined.
• the bar is removed from the PE bag, a slice is separated from the polycrystalline bar and fed to the FTIR measurement.
• the carbon concentration is determined.
• the remaining rod is preferably converted by means of FZ into a monocrystalline rod.
• the concentration of dopants is determined by means of photoluminescence.
• the second rod is preferably passed through the plants for producing polycrystalline silicon fracture (comminution, packaging) and optionally through the plants for the purification of polycrystalline silicon fracture.
• the rod absorbs the impurities with respect to dopants and carbon when passing through the systems.
• the contaminated rod After passing through the cleaning equipment or the road to produce unpurified poly-break the contaminated rod is preferably again packaged in a high-purity PE bag.
• dopants are determined by means of photoluminescence and carbon by means of FTIR.
• the determination of the carbon concentration by means of FTIR does not take place on a polycrystalline disc but on a monocrystalline disc.
• the values measured on the first bar are subtracted from the values of the second bar passed by the facilities.
• the difference values between the first and second bars then give the value that can be assigned to the surface of the polycrystalline silicon after processing, cleaning, packaging.
• the method according to the invention thus offers the possibility of indirectly determining how polysilicon is contaminated in the processing steps such as comminution, cleaning, packaging or transport processes on the surface.
• the process thus provides surface contamination for all sorts of products, such as polysilicon rods, cutrods and polysilicon fractions of different size classes (etched or unetched).
• the dopant concentrations were determined by means of photoluminescence.
• the twelve brother rods - although they come from different batches - must have the same analytical values for boron, phosphorus, aluminum and arsenic, since they were simultaneously driven through the cleaning system under the same conditions.
• Table 1 shows the values determined for boron, phosphorus, aluminum and arsenic in ppta.
• the content of carbon particles on the silicon surface can also be determined with a reproducibility of +/- 10 ppba with a detection limit of 10 ppba.
• the example shows how the second rod is passed through the cleaning system and then examined for dopant concentration.
• the first rod (brother rod of the second rod from a U-shaped body after deposition) was analyzed for dopants by photoluminescence as described above.
• the PE bag in which the second rod (length 20 cm, diameter 1.6 cm) was packed, is opened with a pair of scissors, preferably a ceramic scissors.
• the rod is removed, using a high-purity glove for manual removal. Then the rod is placed in a process bowl.
• PET-Tyvek® glove A suitable high purity glove (PE-Tyvek® glove) is disclosed in U.S. Patent No. 5,348,866 US 2011-0083249 , which is hereby incorporated by reference.
• Tyvek ® from DuPont is a paper-like nonwoven fiber textile function of thermally welded fibers of high density polyethylene (HDPE).
• the process bowl filled with the rod is moved through the cleaning system.
• the silicon rod is washed in a pre-cleaning with an oxidizing cleaning solution containing the compounds hydrofluoric acid (HF), hydrochloric acid (HCl) and hydrogen peroxide (H 2 O 2 ).
• HF hydrofluoric acid
• HCl hydrochloric acid
• H 2 O 2 hydrogen peroxide
• the bar is washed with a cleaning solution containing nitric acid (HNO 3 ) and hydrofluoric acid (HF).
• HNO 3 nitric acid
• HF hydrofluoric acid
• the rod After cleaning the rod, it is dried and, after cooling, handled with a high-purity glove, preferably a PE Tyvek® glove, and packed in a high-purity PE bag and sealed.
• a high-purity glove preferably a PE Tyvek® glove
• the contaminated rod is processed by FZ to a monocrystalline rod.
• dopants are determined by photoluminescence.
• FTIR could also be used to study carbon.
• the difference values between the first and second bars then give the values that can be assigned to the surface of the polysilicon.
• Table 2 shows the determined difference values for surface contamination on boron, phosphorus, aluminum and arsenic. ⁇ b> Table 2 ⁇ / b> B P al ace 44.06 15.46 0.03 1.29 119.32 405.97 194.63 22.78 19.10 4.28 0.89 4.66 128.55 250.91 145.57 17.18 7.70 79.68 0.87 0.52 3.58 21,01 1.53 2.66 3.86 16.17 6.71 4.39 6.57 0.22 0.25 1.24 9.11 2.68 1.37 1.08 10.10 1.37 14,60 0.59 20.47 41.02 7.26 3.18

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• 2012
  • 2012-01-24 DE DE102012200994A patent/DE102012200994A1/de not_active Withdrawn
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• 2013
  • 2013-01-10 CN CN201310009169.9A patent/CN103217396B/zh active Active
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